Clinical Procedure - Visit 2
Confirm Shade Selection
In the early days of veneers, either a no-preparation or minimal tooth preparation, not extending into the dentin, was suggested.2,4,5 This is once again gaining popularity with certain companies. Dentists routinely remove at least 0.5 mm-0.8 mm of enamel. Removal of some enamel aids in achieving better bond strength,6,7 but care must be taken not to remove more than 0.5 mm-0.8 mm, especially in the proximal and cervical areas. Even though dentin adhesives have improved dramatically, porcelain bonding to enamel is better than porcelain bonding to dentin.8
Depth Guide Cuts – Prior to preparation always examine study models in order to avoid over-reducing areas of the tooth that may be rotated or lingually inclined. Hence, the use of a reduction guide is recommended. A diamond depth cut bur can be used to scribe horizontal depth cut grooves on the labial surface of any anterior tooth. Extend these grooves from mesial to distal, taking care not to damage the adjacent teeth that are not being prepared. It may be necessary to angle the bur in relation to the contour of the labial surface to achieve the appropriate depth for these guide cuts. The finish line of the preparation could end gingivally or supragingivally, approximately 0.5 mm incisal to cemento-enamel junction (CEJ). Do not place your gingival depth cut so as to cut into the CEJ area.
Labial Reduction – Using a tapered diamond, reduce the remaining labial tooth structure between the depth cuts. Simultaneously create a chamfer ending 0.5 mm incisal to the CEJ. This reduction should also extend interproximally. Opening the interproximal contact with the adjacent tooth is often preferable to better approximate the veneer and have a clear finish line in the master impression. In cases with mobile teeth and those having recently having completed orthodontics it may be advisable to not pass through the contact areas to prevent tooth movement during temporization.
Types of Veneer Preparation
Incisal Chamfer Preparation (Interlock prep) The incisal edge is not reduced in length. This type of preparation is often used on cuspids and is done in order to preserve the natural guiding palatal surface of the tooth, which is important functionally. Add an additional space for the incisal porcelain by creating a chamfer along the facial incisal margin using the tip of a tapered diamond (Figure 3).
Tooth #6 – Incisal Chamfer Preparation (Interlock Prep)
Tooth #7 – Incisal Butt-joint Preparation
Tooth #8 – Incisal Lingual Wrap Preparation
Tooth #9 – Depth Cut
Incisal Butt-Joint Preparation Prepare 0.5 mm depth cut grooves in the incisal edge. Using the tapered diamond removes the remaining incisal tooth structure. Then round the facial incisal line angle leaving a butt-joint margin along the lingual incisal edge. The incisal reduction should be 0.5 mm-1.0 mm. This type of preparation is done in order to increase the length of the tooth. The length can be increased from 0.5 to 2 mm only.
Incisal Lingual Wrap Preparation Prepare 0.5 mm depth cuts in the incisal surface of tooth. Reduce the incisal surface in a manner similar to incisal butt-joint preparation. Reduce the mesial incisal and the distal incisal corners an additional 0.5 mm. Then using a diamond bur, extend the incisal chamfer to the palatal surface. This palatal chamfer should be a straight line mesial to distal. All incisal edges should be rounded. The lingual chamfer line on the wraparound preparation should be above or under the centric lingual contacts to avoid occlusal contact on the interface between porcelain and tooth structure. Contact should be either all on porcelain or on tooth structure. The incisal wrap prep is a popular option for several reasons. It can be used in most patients, easily fabricated by the technician and easily handled by the dentist due to positive seating on delivery (Figure 4).
Tooth #7 Incisal Lingual Wrap Preparation
The path of insertion for veneers is in the labial or incisal-labial direction. All undercuts and unsupported enamel in relation to this path must be removed. A silicone reduction guide is used in order to check the amount of reduction required. The reduction guide is designed to evaluate the amount of reduction at the incisal, middle third and cervical third of the tooth. Use of a reduction guide is particularly important when teeth are misaligned (Figures 5 & 6).
Strip contact area using a finishing strip prior to impression to improve visualization for lab technician.
Place a # 0 cord to reveal the margin, which is left in place while taking the impression.
Either polyether or polyvinyl siloxane impression materials can be used according to manufacturer’s instruction.
A detailed prescription is written to the laboratory technicians. The prescription should include:
Teeth number, required shade, stump shade.
The type of ceramic required to make the veneers.
If any changes in anatomy are required for the final result, e.g., increasing length.
Make a note of any requests made by the patient.
A pre-impression is usually taken prior to temporization and is used as a template for the provisional restorations.
During the period a patient is in provisional veneers there is a likelihood of postoperative sensitivity. Therefore application of a desensitizer, such as GLUMA, is recommended before the fabrication of the provisionals in order to reduce the sensitivity.
Different techniques are used to fabricate provisional veneers. We recommend using a silicone putty impression material shell in order to fabricate temps, since it reproduces the wax up or study models very accurately.
A bis-acrylic temporary material with the required shade is used. The provisional is not removed but is rather “locked in” as a result of shrinkage. The provisionals are then finished and polished in place. Evaluation of tooth reduction is confirmed by examining the provisionals for thin areas. Although it is unlikely to occur while using the reduction guide, it is sometimes necessary to re-prep under-reduced areas. If this does occur, then you must reimpression and retemporize the prepared teeth.
When fabricating a provisional for a peg lateral or any single tooth veneer, a free-hand composite veneer can also be used.
To maintain good periodontal health, the patient is told to irrigate the marginal area with a chlorhexidine rinse using an endodontic irrigating syringe.